A constitution in which a planetary gear speed reducer is mounted to an axial type motor and a radial type motor to obtain large torque at low speed is conventionally known, and a motor with a speed reducer in which a motor and a planetary speed reducer are combined is known (for example, refer to the last line of left column on page 1 to line 5 from the bottom of right column on page 1, and FIG. 1 and FIG. 2 of Japanese Patent Publication No. 42-24608, and line eight from the bottom of left column on page 1 to line 8 of left column on page 2, and FIG. 1 to FIG. 3 of Japanese Patent Publication No. 50-14696). A motor with a planetary gear speed reducer with combination of an axial type motor and planetary gear trains of two stages, and the like are used.
Since the basic constitutions of the motors with the speed reducers described in the above-described both Patent Publications are the same, the constitution described in Japanese Patent Publication No. 42-24608 will be explained with use of FIGS. 3 and 4. A plunger 43 sliding in a radial direction inside a cylinder block 42 is pressed by pressure oil supplied from an inlet and discharge port 41 provided at a housing 40. In this situation, an inner circumference surface of a rotary block 46 supported at an eccentric cam 44 with a bearing 45 is pressed by the plunger 43 to rotate the rotary block 46.
A pinion 47 with teeth being cut is formed on an outer circumference surface of the rotary block 46. The pinion 47 is meshed with an internal gear 48 formed integrally with the housing 40, and rotation with a center O2 as a center of rotation of the eccentric cam 44 is restrained, and by this restraint, the rotary block 46 revolves. Since a pintle 49 rotates integrally with the eccentric cam 44, pressure oil can be fed to each cylinder alternately corresponding to the rotation of the eccentric cam 44 and the inner circumference surface of the rotary block 46 is pressed via the plunger 43 to revolve the rotary block 46.
From the relationship of a number of teeth Z1, of the pinion 47 and a number of teeth Z2 of the internal gear 48, the rotary block 46 rotates on its own axis by (Z2−Z1)/Z1 with respect to one revolution. From this, rotation of the rotary block 46 can be reduced at a ratio of (Z2−Z1)/Z1, and the reduced rotation can be taken out from an output shaft 51 via a rotation driving pin 50. The output power of the motor with the speed reducer can be taken out as rotation of the output shaft 51 by decelerating the rotation of the motor by the pinion 47 and the internal gear 48. However, a planetary gear train of one stage is used for decelerating the motor rotation, and the number of teeth of the number of teeth Z1 of the pinion 47 and the number of teeth Z2 of the internal gear 48 is made small, whereby a large speed reduction ratio is obtained.
Consequently, when large torque at low speed is to be obtained, a load applied between the pinion 47 and the internal gear 48 becomes large, and breakage occurs to the pin 50 and the like, which causes the situation in which the rotation of the motor cannot be taken out. Consequently, as the torque which can be taken out with the output shaft 51, large torque cannot be taken out, and the torque which can be outputted is naturally limited. The output power is taken out as the shaft rotation of the output shaft 51, and for example, in traveling equipment including a track shoe of an endless track, the output power cannot be taken out in a state of case rotation as an output power to a traveling drive sprocket for driving the track shoe.
In order to take out rotation in the state of the case rotation, a gear mechanism for further making case rotation is required, and especially in order to drive a traveling track shoe with the traveling drive sprocket, output of large torque is demanded. Namely, in order to output large torque, it is necessary to increase the motor in size. Due to this, the upsized motor and the speed reducer cannot be placed within the width of the track shoe, or within the rotation surface of the traveling drive sprocket.
FIG. 5 shows a prior art example of a motor with a speed reducer in which planetary gear trains of two stages are combined with the axial type motor. High pressure oil discharged from an external hydraulic pump (not shown) is introduced into a plurality of cylinders 60 to reciprocate a piston 61 in each cylinder 60. As a result, the piston 61 slides while pressing a swash plate 63 with a piston shoe 62 rotatably provided at a tip end of the piston 61, and rotationally drives a motor shaft 64-1 which is spline-connected to the cylinder 60. Further, this rotationally drives the rotary shaft (sun shaft) 64-2 which is spline-connected to the motor shaft 64-1.
The rotary shaft 64-2 is a first sun gear 65 in a first stage planetary gear train. A plurality of first planetary gears 66 rotatably supported at a first carrier 67 are meshed with the first sun gear 65, and also meshed with a first internal gear 68 formed at a traveling sprocket 75. The first carrier 67 and a second sun gear 70 located outside the rotary shaft 64-2 are spline-connected, and rotation around the rotary shaft 64-2 in the first carrier 67 is transmitted to the second sun gear 70. The second sun gear 70 is a sun gear in a second stage planetary gear train.
A plurality of second planetary gears 71 rotatably supported at a second carrier 72 are meshed with the second sun gear 70, and also meshed with a second internal gear 73 formed at the traveling drive sprocket 75. The second carrier 72 is fixed to a motor case 76 of the axial type motor, and the rotation of the second carrier 72 is hindered. The rotation which is outputted from the axial type motor is taken out by the rotary shaft 64-2. The rotation of the rotary shaft 64-2 is decelerated by the first stage planetary gear train with the rotary shaft 64-2 as the first sun gear 70. Since the traveling sprocket 75 is meshed with a track shoe 77, a heavy load is applied at the time of start, and the first internal gear 68 is in a stopped state.
Consequently, the first planetary gear 66 revolves while rotating on its own axis along the first internal gear 68. The revolution of the first planetary gear 68 is taken out as the rotation of the first carrier 67. The rotation of the first carrier 67 is transmitted to the second sun gear 70. As a result, the rotation which is outputted from the rotary shaft 64-2 is decelerated by the first stage planetary gear train, and is transmitted to the second sun gear 70 of the second stage planetary gear train.
The rotation of the second sun gear 70 rotates the second planetary gears 71 on its own axis. Since the second carrier 72 supporting the plurality of second planetary gears 71 is fixed to the motor case 76 of the axial type motor, the second planetary gears 71 do not revolve, but only rotate on their axes. By the rotation of the second planetary gears 71, the second internal gear 73 formed at the traveling drive sprocket 75 rotates, and drives the track shoe 77 which is meshed with the traveling drive sprocket 75. As a result, the rotation outputted from the rotary shaft 64-2 is decelerated by the first stage planetary gear train, and after it is further decelerated by the second stage planetary gear train, it drives the traveling drive sprocket 75. After the traveling sprocket 75 is driven, the first internal gear 68 integrated with the second internal gear 73 also rotates in a rotating direction of the traveling drive sprocket 75.
However, the axial type motor with the speed reducer with the above-described constitution is long in the length in an axial direction. In addition, in the axial type motor, the speed reduction ratio in the first stage planetary gear train generally has to be made large to perform high-speed rotation, and therefore there arises the problem that the placement constitution of the planetary gear train is limited.